Location systems can be used in sites to locate an asset in a defined area. Such asset could be a piece of equipment, a person, etc. Some location systems can show the real time location of an asset but also the exact room number in which it is located at a given time with high reliability. This is specifically required in large building floor areas that are divided into many small rooms such as in hospital buildings.
U.S. Pat. No. 6,963,289, which is hereby incorporated by reference, teaches an exemplary wireless local area network (WLAN) real time location system (RTLS). Such system may include a radio frequency identification (RFID) tag that transmits RF signals on a WLAN channel in order to allow the tag's location to be calculated. This is typically done using RSSI (receive signal strength indication) or TOA (time of arrival) measurements of the radio signal that is transmitted by the tag. The signal is received by several location receivers and/or WLAN access points that are in different positions, and special mathematical algorithms are implemented to calculate the tag's location. Further elaboration of these systems and methods can be found in U.S. Pat. No. 6,968,194 and US Patent Publication No. 2004/0203870, which are hereby incorporated by reference.
Such systems may also include a low frequency transmitter (sometimes referred to as an “exciter”), which periodically transmits a beacon signal. Such beacon signals may include a room or exciter ID information. Such an exciter may be positioned at the entrance to a room or at a perimeter boundary, so that it triggers every tag that enters or leaves the room or the perimeter boundary. When the tag receives the beacon signal, it transmits a WLAN message that reports the room and/or exciter ID information to the location system. Further elaboration of these systems and methods can be found in U.S. Pat. No. 7,403,108, which is hereby incorporated by reference.